REST API: Clean up argument and property types.

There's a couple of places where we were missing type notes for arguments, which mainly affects documentation.

Props jnylen0.
Fixes #38792.

Built from https://develop.svn.wordpress.org/trunk@39250


git-svn-id: http://core.svn.wordpress.org/trunk@39190 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/version.php

@@ -4,7 +4,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '4.7-beta3-39249';
+$wp_version = '4.7-beta3-39250';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.